Despite two decades of persistent research on prophylactic and therapeutic immunization against HIV, an effective vaccine-based solution to the HIV pandemic has remained elusive. However, the last few years have provided important insights into the type of immune response that would be required for an effective HIV vaccine. For instance, in studies of natural HIV infection, T cell responses to the Gag protein are associated with lower viral load, and nonhuman primates (NHP) that mount robust Gag-specific T cell responses after immunization are more likely to survive after challenge with SIV. Immune Design Corp (IDC) is developing a vaccine platform around a novel DC-targeting non-integrating lentivector (DC-NILV). Using this delivery system, one can efficiently express antigens in DCs and elicit unprecedented CD8 T cell immune responses after a single administration. The ultimate goal of this project proposal is to establish a foundation for a DC-NILV-based HIV vaccine by developing and testing a DC-NILV SIV vaccine analogue for use in future NHP-SIV challenge studies. To accomplish this goal, we have chosen SIVMAC251-Gag and -Nef antigens encoded and delivered by our DC-NILV platform as vaccine candidates. To initiate this work, we will first develop a mid-scale DC-NILV production process based on the small-scale process currently in place, while establishing product release assays to assess vector quality and safety. Once these processes are established, we will optimize vaccine delivery for maximal immunogenicity in mice using assays that measure CD8 and CD4 T cell responses against SIV-Gag and -Nef. Finally, we will test the immunogenicity of SIV-Gag and -Nef when delivered via our vaccine platform in rhesus monkeys. During the course of the study, significant emphasis will be placed on the magnitude, breadth, and polyfunctionality of the ensuing immune responses as these characteristics are currently perceived to be the best correlates for long-term protective T cell-mediated immunity. The overall success of the study will primarily be measured using the following criteria: 1) The delivery of SIV antigens via DC-NILV provides and effective mechanism to generate CD8 T cell responses in NHP;2) There is value in homologous DC-NILV prime-boost vaccine regimens for the generation of protective T cell-mediated immunity;and 3) The inclusion of multiple antigens within a single DC-NILV is able to expand the diversity of the ensuing immune response without compromising the response against individual protein antigens. PUBLIC HEALTH RELEVANCE: There is an unmet medical need for an effective vaccine against HIV as previous attempts have failed, most likely due to their inability to induce protective T cell responses. We are developing a novel vaccine vector that leads to robust T cell activation by delivering antigens directly to dendritic cells, the key cell type for initiation of adaptive immunity and memory. This vaccine vector has the potential to have great protective efficacy against HIV infection in humans.